Dynamic Control of Oxygen Diffusion Resistance in Nodules

Abstract

Excess inputs of O₂ to infected cells of legume nodules will lead to loss of nitrogenase activity (Witty et al., 1986), whilst insufficient O₂ initially curtails N₂ fixation and eventually causes oxidant-induced nodule senescence (Escuredo et al., 1996). There is now a considerable weight of evidence showing that the O₂ supply to N₂-fixing bacteroids is controlled by a variable physical barrier to diffusion which balances O₂ influx with its respiratory consumption. However, some workers have suggested biochemical/metabolic alternatives which might substitute for a physical barrier.